1. Field of the Invention
This invention relates generally to a porcelain clad, gas, circuit interrupter for a power line or circuit, and more particularly, to such a circuit interrupter of the type in which an insulating operation rod is disposed in a support porcelain tube supporting an arc extinguishing porcelain tube defining therein an arc extinguishing chamber in which a stationary and a movable contact are accommodated, the operation rod being adapted to open or close the movable contact against the stationary contact and provided at its opposite ends with a pair of shield members.
2. Description of the Prior Art
A conventional porcelain clad, gas, circuit interrupter is shown in FIG. 3. In this Figure, reference numeral 1 designates an arc extinguishing porcelain tube defining therein an arc extinguishing chamber (15) in which a movable contact 14 and a stationary contact (16) are accommodated. The arc extinguishing porcelain tube 1 is supported by a support porcelain tube 2 in which an insulating operation rod 3 is disposed for operating the movable contact (14) in the arc extinguishing chamber (15) for opening and closing it with the stationary contact (16) for interrupting a power circuit or line. The support porcelain tube 2 has an upper flange 2a and a lower flange 2b formed at the upper and lower ends thereof, the upper flange 2a being provided with a connector flange 4 adapted for connection with a connector flange 1a of the arc extinguishing porcelain tube 1. The insulating operation rod 3 is connected at its upper end adjacent the arc extinguishing porcelain tube 1 by means of, for example, a connector pin 7a with a socket end 5a of a rod 5 leading to the movable contact in the arc extinguishing porcelain tube, and at its lower end by such as a connector pin 7b with a socket end 6a of a rod 6 leading to a drive source. The socket end 5a of the rod 5 is formed of an electrically conductive material and serves as an upper shield for alleviating or diminishing the strength of electric field affected by the upper flange 2a and the connector flange 4 of the support porcelain tube 2. Similarly, the socket end 6a of the rod 6 is formed of an electrically conductive material and serves as a lower shield for alleviating or diminishing the electric field affected by the lower flange 2b of the support porcelain tube 2. The arc extinguishing porcelain tube 1 and the support porcelain tube 2 are filled with an electrically insulating gaseous medium 8 such as SF6 gas. Reference numeral 9 designates equipotential surfaces.
In such a conventional porcelain clad, gas, circuit interrupter, however, the upper and lower shield members 5a, 6a include pointed edges or sharp projections. Accordingly, when a voltage of a predetermined value is imposed across the stationary and movable contacts (14) in the arc extinguishing porcelain tube 1, the strength of electric field thus created is the highest at the distal end of the upper shield member 5a, which acts as an internal electrode. For this reason, it is desired that the distal end of the upper shield member 5a be configured into a round shape or into a gradually changing shape so as to reduce the electric field strength. On the other hand, the porcelain tubes 1 and 2 have to be reduced in size for the purposes of cutting down production costs, as a result of which it becomes difficult to maintain a certain minimum distance required for electrical insulation between the upper shield member 5a and the inner side surface of the support porcelain tube 2.
The conventional porcelain clad, gas, circuit interrupter as constructed in the above-described manner has involved the following problems. Specifically, when a high voltage is imposed across the stationary and movble contacts (not shown) in the arc extinguishing porcelain tube 1, the density of the equipotential surfaces (or the electric flux density) becomes higher at that portion of the support porcelain tube 2 near the distal end of the upper shield member 5a so that the electric field strength along the surface of that portion of the support porcelain tube 2 is extremely large. Consequently, the support porcelain tube 2 must have an extremely high resistance to voltage and to this end, it is necessary to increase the diameter of the support porcelain tube 2, thus resulting in an increase in overall size and production costs.